1. Field of the Invention
This invention relates to exposure systems and more particularly to methods and apparatus for exposing a workpiece to radiation defining a pattern.
2. Description of Related Art
Disadvantages of comparable prior art are that a conventional stepper uses a fixed chromium (Cr) pattern binary mask. A mask which is both defect free and which has the exact Critical Dimension (CD) is very difficult to make. To produce one chip, normally many masks are needed for the required layers. For optimization of the photolithographic process employed, a few modifications of the mask at different time are required. In addition, many wafers require optimization of stepper parameters such as focus, energy, NA (Numerical Aperture), and dose.
Pfauler et al. "High-Throughput Optical Direct Write Lithography", Solid State Technology (June 1997), pp. 175-176, 178, 180, 182 describes a direct write lithography system using a programmable phase-modulated spatial light modulator (SLM) system in which the image is reflected from the SLM onto a semiconductor wafer. The spatial light modulator comprises an array of rectangular electrodes with a reflective, deformable viscoelastic layer on top. The SLM serves as a plane mirror in an optical system.
U.S. Pat. No. 5,701,185 of Reiss et al. for "Spatial Light Modulator Assembly for Adapting a Photographic Printer to Print Electronic Images" shows use of a SLM for a photographic printer.
U.S. Pat. No. 4,846,694 of Erhardt for "Computer Controlled Overhead Projector Display" in which a computer controls a transmissive (transparent or semi-transparent) liquid crystal display overhead projector display.
U.S. Pat. No. 3,824,604 of Stein for "Alphanumeric Printing System Employing Liquid Crystal Matrix" shows a printing system using a LCD matrix.
U.S. Pat. No. 5,028,939 of Hornbeck for "Spatial Light Modulator System" shows a SLM.
U.S. Pat. No. 5,083,854 of Zampolin et al. for "Spatial Light Modulator with Improved Aperture Ratio" shows a SLM with improved aperture ratio.
U.S. Pat. No. 5,576,562 of Komuma for "Solid-State Imaging Device" shows an imaging device using photodetectors arranged in a matrix array and a CCD.
U.S. Pat. No. 5,629,113 of Watanabe for "Photomask Used by Photolithography and a Process of Producing Same" shows a photomask and process for making the photomask.